Myoglobin and hemoglobin contain ferrous iron (Fe2+), which normally transports reversibly bound oxygen molecules to tissues. When muscle or red blood cells are damaged, the iron-chelating heme molecules are released into the plasma, and the ferrous iron is oxidized to the ferric (Fe3+) state. In the higher oxidation state, the ferric hemoproteins are able to reduce other molecules, notably hydrogen peroxide and lipid hydroperoxides, producing lipid peroxides and ferryl (Fe4+) hemoproteins. The ferryl hemoproteins can then enter an oxidation-reduction cycle with lipid molecules, causing further lipid peroxide production, leading to a cascade of oxidative damage to cellular membranes (10-12).